The invention relates to a charging system for charging chambers of a rotating clutch assembly.
Many automatic transmissions for motor vehicles use rotating clutch assemblies to control gear ratio changes. A typical clutch assembly includes a clutch pack or clutch having multiple plates, and the clutch is moveable between a clutch disengaged position and a clutch engaged position in which the plates are frictionally engaged with each other. The assembly further includes a housing and a clutch piston disposed in the housing and engageable with the clutch for urging the clutch toward the clutch engaged position. The housing and clutch piston cooperate to define a clutch apply chamber or clutch chamber, which is filled with pressurized fluid when the clutch is to be moved to the clutch engaged position.
When the clutch moves back to the clutch disengaged position, all of the fluid is not exhausted from the clutch chamber. Therefore, as the housing continues to rotate, centrifugal pressure builds up behind the clutch piston. The centrifugal pressure imparts a force on the clutch piston, and the force, if not counteracted, may cause the clutch to unintentionally move to the clutch engaged position.
One approach for counteracting this force includes providing a compensator chamber or balance chamber on a side of the clutch piston opposite the clutch chamber. The balance chamber is charged with low pressure lube oil, which is supplied by a pump, so as to build up a compensation pressure in the balance chamber.
Because the flow rate of lube oil is low and relatively constant, it may be difficult to maintain sufficient compensation pressure in the balance chamber during shift events. Furthermore, because lube oil is only fed to the balance chamber, a pressure differential typically develops between the balance chamber and the clutch chamber. This pressure differential results in a net static force acting on the clutch piston. During a shift event, higher pressure must then be developed in the clutch chamber in order to overcome the static force. As a result, fuel economy is reduced.
The invention addresses the shortcomings of the prior art by providing a clutch assembly and charging system combination for use with an automatic transmission. The combination includes a clutch assembly having a clutch that is movable between a clutch engaged position and a clutch disengaged position. The clutch assembly further includes a clutch piston that is engageable with the clutch for urging the clutch toward the clutch engaged position, a clutch piston chamber in fluid communication with one side of the clutch piston, and a compensator chamber in fluid communication with an opposite side of the clutch piston. The combination further includes a charging system having a fluid circuit that is in fluid communication with the clutch piston chamber and the compensator chamber. The fluid circuit is configured to receive exhaust oil from the transmission, and to charge the clutch piston chamber and the compensator chamber using the exhaust oil.